1. Field of the Invention
The present invention relates to a torsional quartz crystal resonator. More specifically, the invention relates to the cut angle, thickness-to-width ratio, shape and excitation electrode structure of a torsional quartz crystal resonator of the specific cut type referred to as "TT cut" in this description. The present invention particularly relates to the torsional quartz crystal resonator of the type suitable for a clock signal source in various portable devices such as a wrist watch, a pager, an IC card and a vehicle wireless communication implement, in which the resonator is required to have a high level of accuracy, a compact size, good resistance to shock and a reasonable price.
2. Description of the Prior Art
There has been used in the prior art a flexural mode quartz crystal resonator of a tuning fork type, and a length extensional mode quartz crystal resonator in a frequency band of 200 kHz-600 kHz. However, the flexural mode quartz crystal resonator of the tuning fork type utilizes an overtone, and hence formation of electrodes is complicated and a serious loss of vibrational energy is caused through lead wires, etc. Consequently, this type of resonator has the drawback of a relatively high series resistance R.sub.1. On the other hand, the extensional mode quartz crystal resonator has an oscillating frequency which is reciprocal to a length of a vibrational arm of the resonator. Therefore, the resonator is enlarged in the relatively low frequency range below 600 kHz, thereby causing the drawback that the ability scale-down the resonator in size is difficult. In view of these drawbacks, there has long been desired a quartz crystal resonator of a new cut type which would feature an oscillating frequency in the range of 200 kHz-600 kHz, a micronized compact size, a zero temperature coefficient, and an easy chemical etching process.